Owing to their unique ability to dissolve lignocellulosic biomass and related carbohydrates under relatively mild conditions, plus several other concurrent advantages (e.g., as designable and recyclable solvents with low volatility and toxicity), ionic liquids (ILs) such as 1-alkyl(R)-3-methyl(M)imidazolium(IM) chloride salts, [RMIM]Cl, have attracted rapidly growing interest, particularly in the pursuit of renewable energy and sustainable chemicals from plant biomass. For instance, ILs have enabled homogenous hydrolysis of cellulose to sugars in high to quantitative conversion, in the presence or absence of catalyst, and catalyzed conversion of glucose or cellulose into the biomass platform chemical 5-hydroxymethylfurfural (HMF), a key and versatile biorefining intermediate for value-added chemicals and liquid fuels. Upgrading of HMF can be achieved by metal-catalyzed transformations such as hydrogenation/hydrogenolysis into 2,5-dimethylfuran, a liquid fuel with a 40% higher energy density than ethanol, and aldol condensation with organic compounds followed by dehydration/hydrogenation into C9 to C15 liquid alkanes (fuels), thus upgrading it into the kerosene/jet fuel range (C8 to C16). Direct coupling of two HMF molecules would make a C12 biofuel intermediate, but HMF or furfural cannot undergo aldol self-condensation because they possess no α-H.
Accordingly, new methods are needed for upgrading HMF into useful intermediates and products. New methods for coupling HMF would provide such valuable intermediates for use as products such as chemicals for synthetic chemistry and liquids for jet or diesel fuels and the like.